Well, who knows? Apparently not even George R.R. Martin! “I don’t know. No one knows.”
According to the big guy himself, in his blog, while there might be up to ten series, HBO is planning for 7.
“I do know that David & Dan have stated in interviews that they see the show winding up in seven seasons. People send me emails about that every time I say “I don’t know” in response to the question, as if I were somehow unaware of what D&D have said. I’m not.
I also know that HBO wants the series to run longer than that. I have known that since the very beginning… well, actually, since the day after the second episode of season one aired, when I had lunch with one of HBO’s top execs, who told me, “We want this to run ten years.” I allowed that ten years sounded fine to me. I continue to hear similar sentiments from HBO every time I have meeting with them, be it in LA or New York. “
By contract, HBO has only thus far committed to 6 seasons. Television and film, being the industries they are, have funny things happen, so whether we will have Game of Thrones gracing our screens longer than that is pure speculation but I, for one, am waiting for the next two guaranteed seasons with baited breath.